7 88 THE POPULAR SCIENCE MONTHLY. 



ing that steam-power is substituted for the manual labor you just saw 

 for producing the electric currents. 



We next come to the work performed by electricity in passing 

 through solids. The result of that work is simply the production of 

 heat. Before me you will notice two brass stands, and between them 

 I will suspend a piece of fine platinum wire. I now join up one of my 

 battery wires to one of the brass stands, and touch the other brass 

 stand with the other battery wire ; the effect appears as a red glow in 

 the platinum wire. If I bring one of my battery wires from the bot- 

 tom of the brass stand to the end of the platinum wire, the color of 

 the glow becomes brighter ; and, as I move my battery wire along the 

 platinum wire, the glow or light produced by the high temperature in 

 the platinum becomes more and more intense, until finally, when it 

 reaches a certain temperature (about 3,000 Fahr.), the wire is rup- 

 tured, and falls to the ground. That is evidence that the passage of 

 electricity, through solid conductors, produces heat, and the amount 

 of heat produced is proportioned to the work done in the battery. 

 Energy expended in one part of a circuit must be given out at another. 

 If zinc is consumed in a battery, it generates a certain amount of 

 energy ; that energy must be evident in some other part of the circuit, 

 and the heat you saw in the platinum was really the heat that would 

 have appeared in the battery itself if we had not caused the current 

 to flow through a solid conductor which offered a considerable amount 

 of resistance to its progress, as compared with the resistance in the 

 battery itself. This power of producing heat has been utilized in 

 various ways, such as for firing fuses. [An Abel fuse was exploded.] 

 At many places throughout the country, time-guns are fired by such 

 an electric fuse to announce the Greenwich time current at a certain 

 hour. Mines and torpedoes are exploded in a similar manner ; quar- 

 ries are blasted, and many other results are brought about by pass- 

 ing electricity through platinum wire placed in explosive substances, 

 or by special fuses. I do not intend to frighten or alarm you, but for 

 your amusement, and through the kindness of Professor Abel, I have 

 had fuses fixed out of harm's way at various points round the room, 

 and, when a small current is passed through them, you will hear the 

 explosion produced. Those fuses might have been fixed miles away, 

 and the same effect would have been produced, and from it you will 

 understand how a number of charges can be fired, or a number of 

 guns can be discharged simultaneously on board our large men-of-war. 



The next branch of the subject is the work done by electricity in 

 its passage through air and gases. I have shown you that, in its pas- 

 sage through liquids, it tears the constituents of the solution asunder ; 

 in its passage through solids heat is produced ; and in its passage 

 through air, it not only produces heat, but violent projection of mate- 

 rial particles as well, which it renders incandescent, producing sparks, 

 heat, and other disruptive effects. To illustrate this, I have provided 



